This disclosure relates to a downstream portion of a diffuser used to provide diffuser flow to various components of a gas turbine engine, for example, for cooling.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section.
Historically, a fan in the fan section was driven at the same speed as a turbine within the turbine section. More recently, it has been proposed to include a gear reduction between the fan section and a fan drive turbine. With this change, the diameter of the fan has increased dramatically and a bypass ratio or volume of air delivered into the bypass duct compared to a volume delivered into the compressor has increased. With this increase in bypass ratio, it becomes more important to efficiently utilize the air that is delivered into the compressor section. Military engines also benefit from effective use of compressed air.
One factor that increases the efficiency of the use of this air is to have a higher pressure at the exit of a high pressure compressor. This high pressure results in a high temperature increase. The temperature at the exit of the high pressure compressor is known as T3 in the art. T3 air may be used to supply fluid to a diffuser case surrounding a combustor housing in the combustor section to diffuse the compressed air entering the combustor housing. Super-cooled fluid from a heat exchanger may also be used, or used as an alternative to T3 air, to provide a diffuser flow around the combustor housing.
It may be desirable to use diffuser flow for other purposes. Pulling air from large bosses on the diffuser case, over the combustor or first vane, leads to local pressure drops. These pressure drops can greatly affect the dilution effectiveness (pattern factor) of the diffuser flow and vane cooling which both can lead to durability issues for the turbine section due to local hot spots.